The semiconductor chips are typically provided on a foil held in a frame, which is also known as a tape in the field, for the purpose of processing on a semiconductor mounting device. The semiconductor chips adhere to the foil. The frame with the foil is received by a displaceable wafer table. The wafer table is displaced in cycles in order to provide one semiconductor chip after the other at a location and the semiconductor chip which is then provided is received by a chip gripper and placed on a substrate. The removal of the provided semiconductor chip from the foil is supported by a die ejector which is arranged beneath the foil. The die ejector is a table with a supporting surface on which the foil is disposed. The table contains a plurality of holes in order to fix the foil during the detachment process of the semiconductor chip by means of vacuum.
In many cases, one or several needles arranged in the die ejector will support the detachment of the semiconductor chip from the foil. Needle-supported methods are known from a large number of patents, e.g. from US 20040105750 or U.S. Pat. No. 7,265,035. In US 2008086874, the die ejector comprises a block with a plurality of rods which have a flat end and a second block with a plurality of needles, with the needles being arranged between the rods and the surface of the flat end of each rod having a multiple of the cross section of a needle. For the purpose of detaching the semiconductor chip, the block with the rods is lifted at first and the block with the needles is lifted until the needles protrude beyond the rods.
A die ejector with supporting structures is known from WO 2005117072, on which the foil rests during the entire detachment process. The supporting structures are enclosed by rods with a flat end which are displaceable in the direction towards the semiconductor chip as well as in the opposite direction. The supporting structures and the rods can also be formed by a plurality of individual tappet rods which are arranged in the manner of a matrix.
A die ejector is known from US 20050059205 which comprises several plates which are disposed adjacent to one another, and for the purpose of detaching the semiconductor chips are lifted either jointly and then lowered sequentially from the outside to the inside or are lifted from the outside to the inside sequentially in order to form a pyramidal elevation that protrudes beyond the supporting plane.
Various methods are also known in which the semiconductor chip is detached from the foil without the use of a needle. In U.S. Pat. No. 4,921,564, the foil beneath the semiconductor chip is subjected to a vacuum at many individual locations in order to remove the foil at these places from the semiconductor chip. This is also the case in US 20040038498. The chip gripper receives the semiconductor chip only when the detachment process has been completed, which means when the chip ejector is no longer able to continue the detachment process. This method is therefore not suitable for extremely thin semiconductor chips because they would fracture. In EP 1596422, the foil is detached completely from the semiconductor chip by means of a stamp without the assistance of the chip gripper. This method is also not suitable for extremely thin semiconductor chips because they would bend and/or curl up. In US 2002129899 and U.S. Pat. No. 7,238,593, the foil is drawn over the edge of the die ejector and removed thereby. In U.S. Pat. No. 6,561,743, the foil is drawn off in a boundary region of the semiconductor chip by means of vacuum and then displaced relative to the semiconductor chip which is gripped by the chip gripper, with the semiconductor chip being detached from the foil.
The detachment and removal of a semiconductor chip from the foil is known in the field as pick process. A needle-supported standard pick process comprises the following steps:    a) Displacement of the wafer table in order to provide the next semiconductor chip to be received;    b) Fixing of the foil on the chip ejector by means of vacuum;    c) Lowering of the chip gripper until it touches the surface of the semiconductor chip and applying a vacuum to the chip gripper in order to fix the semiconductor chip;    d) Lifting the needles to a predetermined height, with the needles lifting the semiconductor chip and the foil partly detaching from the semiconductor chip;    e) Moving the chip gripper away, with the semiconductor chip detaching completely from the foil and the needles.
The detachment and removal of semiconductor chips from the foil can only be achieved when the adhesive force of the foil remaining after step d) is smaller than the vacuum suction force of the chip gripper. Otherwise, so-called pick errors occur. The semiconductor chip cannot be picked up and very thin semiconductor chips are damaged or broken.
The semiconductor chip is glued together with the substrate during bonding either by means of an adhesive which was applied first to the substrate, or by means of an adhesive film, a so-called “die attach film”, which is applied to its rear side. In the latter case, the semiconductor chip needs to be severed from the foil with the adhesive film. The substrate is heated up to a temperature which is over room temperature in order to produce a permanent adhesive bond between the semiconductor chip and the substrate during bonding. As a result of its contact with the substrate, the adhesive film will melt and tightly glue the semiconductor chip. The chip gripper is heated by this adhesive process that lasts a few seconds. During the next pick process, an undesirable heating of the adhesive film occurs already in the next semiconductor chip to be received during the detachment process. The adhesive force between the foil and the adhesive film will increased, leading to the pick errors as mentioned above.
The term semiconductor chip shall also be understood below as a semiconductor chip whose rear side is coated with an adhesive film.